1. Field of the Invention
The field of the invention relates generally to power production from distributed DC power sources, and particularly to a photovoltaic panel having series connected photovoltaic strings the outputs of which are connected in parallel.
2. Related Arts
The recent increased interest in renewable energy has led to increased research in systems for distributed generation of energy, such as photovoltaic cells (PV), fuel cells, batteries (e.g., for hybrid cars), etc. Various topologies have been proposed for connecting these power sources to the load, taking into consideration various parameters, such as voltage/current requirements, operating conditions, reliability, safety, costs, etc. For example, most of these sources provide low voltage output (normally a few volts for one cell, or a few tens of volts for serially connected cells), so that many of them need to be connected serially to achieve the required operating voltage. Conversely, a serial connection may fail to provide the required current, so that several strings of serial connections may need to be connected in parallel to provide the required current.
It may be also known that power generation from each of these sources depends on manufacturing, operating, and environmental conditions. For example, various inconsistencies in manufacturing may cause two identical sources to provide different output characteristics. Similarly, two identical sources may react differently to operating and/or environmental conditions, such as load, temperature, etc. In practical installations, different source may also experience different environmental conditions, e.g., in solar power installations some panels may be exposed to full sun, while others be shaded, thereby delivering different power output. In a multiple-battery installation, some of the batteries may age differently, thereby delivering different power output. While these problems and the solutions provided by the subject invention may be applicable to any distributed power system, the following discussion turns to solar energy so as to provide better understanding by way of a concrete example.
In view of the above, a newly proposed topology for connecting multiple DC power sources to the load should also lend itself to easy testing and operational verification during and after installation.